Color image reproduction system



June 22, 1954 H. w. LEvr-:RENZ

COLOR IMAGE REPRODUCTION SYSTEM Filed sept. 24. 1949 w gva, lmm MSSSlNVENTOR lvm. .vm Km.

Patented June 22, 1954 ITED STATS TENT COLOR IMAGE REPRODUCTION SYSTEMHumboldt W. Leverenz, iirinceten, N. J., assigner to Radio Corporationof America, a corporation of Delaware 14 Claims. l

The present invention relates to a method and apparatus for producingcolor images, and deals more directly, although not necessarilyexclusively, with a method and apparatus for producing color televisionimages.

The present invention is further concerned with the high efliciency andhigh brilliance re production of color images in television receiversystems.

It is quite well known in the art to which the present pertains thatcolor images may be produced by either the subtractive or additive colorrecord method. The former ci these methods is utilized for the printingof color images or wherever the composite color image is to be viewed byreflected or transmitted White light. The additive method of color imageformation is contrariwise related to the formation of an image which initself is the source of light by which it is visible.

The present invention is more directly concerned With the latter oradditive system of color image production as, for example, employed inpresent-day color television image reproducing systems. ln one or thesimpler and more common forms of television color image reproducingarrangements, the color image is broken up into red, blue and greenadditive complementary color records. These images may then beseparately reproduced by three kinescopes having respective red, blue,and green phosphore and simultaneously viewed by a mirror system whichregisters one image upon another.

Another arrangement for reproducing and combining the red, blue, andgreen records to form the composite color image, is to simultaneouslyproduce each of these color records on a separate kinescope having awhite phosphor or cathodoluminescent material. Appropriate red, blue andgreen filters may then be respectively placed in front of the threekinescopes, and the resulting light images passing through the ltercombined and brought in register by some form of optical system. Insteadof utilizing actual red, blue and green lters, which interpose aconsiderable light loss, the respective white phosphor lainescopes maybe directed into a dichroic mirror arrangement which inherently reiieotsonly the proper color components and combines them to form the compositecolor image.

Alternatively, another arrangement for viewing the red, blue and greencolor records is sometimes referred to as the sequential method whereina single kinescope With a White-emitting phosphor screen is suppliedwith image information sequentially forming on the face thereof, thered,

blue and green color records of the image to be reproduced. There isthen synchronized with the respective formation of these black and Whiteversions of the color records, a rotationally driven iilter device whichimposes suitable red, blue and green lters between the face of the whitephosphor kinescope and the eye so that the eye, through its rather longpersistence of vision, may blend the red, blue and green color recordsand form the illusion of a composite uninterrupted color image.

It is clear that the sequential intel-positioning of suitable colorlters between the face oi the kinescope and the eye also electsconsiderable reduction in the apparent brilliance of the color image soproduced. With the exception of pron viding separate kinescopes havingthe proper red, blue and green phosphore on their targets andsequentially keying these kinescopes or for a period corresponding tothe reception of the corresponding color record information, and thencombining by optical means the color images so formed, there is, atpresent, no Well-known Way for overcoming the undesirable lossesattending the use of the separate additive color filters in sequentialcolor systems.

It is therefore a purpose of the present invention to provide a simpleand economical method and apparatus for producing color images in whichthe use of selective color lters of any character is not required.

It is another purpose of the present invention to provide an improvedand novel method and apparatus for producing color television images bymeans of a single cathode ray image reproducing tube wherein theefficiency of beam energy transfer to visible light corresponding to therequired color records is enhanced to a degree providing much brightercolor images than otherwise obtainable.

1n one of its more general forms, the present invention contemplates theuse of a device for producing a luminescent image Whose radiant energyfalls in the most part, in the ultraviolet region. This image sourcedefines the individual color records by controlling the intensity ofultaviolet radiation over various portions of its image area. Aplurality of photoluminescent targets responsive to the ultravioletradiated by the image source are then provided. Each photoluminescenttarget characteristic is such to generate a respective color rangeembraced by an additive color record upon which the color system isbased, for example, red, blue or green.

In one of its more specific forms, as applied to a sequential type colortelevision receiver, the present invention contemplates the use of asingle kinescope having a primary target or screen area ofcathodoluminescent material adapted to produce a high percentage ofultraviolet radiation when excited by the kinescope electroni beam. Aplurality of photoluminescent targets are then arranged for sequentialexcitation by the ultraviolet radiation emitted by the kinescopecathodoluminescent material. Each photoluminescent or secondary targetis compounded to produce a different given color radiation uponexcitation, this radiation corresponding to a respective additive colorupon which the color television system is based. The high efficiencymanifested in the transformation of the ultraviolet energy to visiblelight energy through the agency of the photoluminescent material resultsin a much higher intensity color image for a given kinescope beamcurrent than heretofore obtainable by systems of equivalent simplicity.

A more complete understanding of the present invention, as well as otherobjects and features of advantage, will become apparent through thereading of the following specification especially when taken inconnection with the accompanying drawings in which:

Figure l is a diagrammatic and block representation of a typicalsequential type television color transmitter;

Figure 2 illustrates one form of the present invention as applied to anotherwise conventional color television receiver adapted to receive andreproduce sequential type color television images;

Figure 2a shows one form of window structure for cathode ray imagereproducing kinescopes particularly suited for use in the arrangement inFigure 2;

Figure 3 shows one form of photoluminescent target suitable for use inthe arrangement shown in Figure 2; and

Figure 4 illustrates a modification of the general arrangement shown inFigure 2.

Turning now to Figure l, there is shown in block form a typical additivetype sequential color television transmitting system. Here an object lilis imaged on the target of electronic scanning device I2, such as animage orthicon, by means of a lens I4. Scanning of the target by theelectron beam within the tube l2 is controlled by means of the camerasweep circuits I6 which excite the deflection yoke I8. Output signalsfrom the scanning tube l2 are then fed to the input of the videoamplifier 28, whose output is in turn applied to a mixer circuit 22. Inorder to provide sequential color records of the object l0, a well-knownform of color wheel or disk 24 may be employed. As is well-known tothose skilled in the art, the disk 24, in one of its more prominentforms, is provided with at least three apertures, such as 26, throughwhich light rays from the object I may reach the target of the scanningtube l2. These three apertures are respectively provided with a red,blue and green filter, such as 28. Since the motor 30 is held insynchronism with the camera sweep circuit by means of the sync generator32 acting through the motor sync `circuit 34, the rotation of the colorfilter disk 24 is such that the respective images scanned by thescanning device l2 sequentially represent red, blue and green colorrecords of the image l0.

In a conventional fashion, the output of the sync generator 32 is alsoapplied to the mixer 22 for mixing with the output of the videoamplifier 20. The composite television signal thus obtained is thenapplied for modulation of the radio transmitter 36.

The receiving system shown in Fig. 2, with the exception of that portionembodying the present invention, is also quite conventional in nature.Signals from the transmitter 36 are intercepted by the antenna 38 andapplied to the input of a television receiver 40. The demodulated andamplified video signal is then applied to a control electrode such as 42of a cathode ray image reproducing tube or kinescope 44. A compositedemodulated signal is also applied to both a sync separator circuit 46whose output in turn controls the beam deflection circuit 48 for theyoke 50, as well as the motor sync circuit 52, for controlling the speedof the motor 54. In prior art arrangements, the screen surface 56 of thekinescope 44 is provided with a cathodoluminescent material excitable bythe electron beam in the kinescope to produce a virtually white light.This material may of course be backed by an electron permeable lightreflective coating such as a 1090 thick lm of aluminum as is well knownin the art. The white image formed thereby is, according to the priorart arrangements, made viewable through a plurality of apertures 58 in acolor wheel 60. These apertures, in accordance with the prior artarrangement, appropriately carry either red, blue, or green filters asdescribed in connection with the scanning arrangement of Figure l sothat corresponding black and white images appearing on the screen of thekinescope 44 are viewed through the iilter of the color representing theparticular color record carried by the image.

f Through the synchronizing circuits provided, the

reproducing color wheel motor t4 is held in synchronism with thescanning lter motor 30 so that the eye 62 will view a sequentialreconstruction of the color image I0.

As pointed out hereinabove, the color filters employed in the apertures58 of the wheel 60 in the television receiver substantially reduce inintensity the light radiated from the screen of the kinescope 44 sincethe spectral band of wavelengths transmitted by each individual filterrepresent only a portion of the entire band of wavelengths radiated bythe cathodolumincscent kinescope screen.

Considering this in another way, the prior art arrangements provide thatthe electron beam within the kinescope 44 excite the cathodoluminescentmaterial 56 on the face of the lrinescope to form an image color record.The cathodeluminescent material is made of a mixture of individualcathodoluminescent materials, each productive of a discrete spectralband of energy. These individual cathodoluminescent materials are sobalanced to produce a virtually white light when excited by the electronbeam. Manifestly, then, virtually all of the energy of the electron beamis transformed into a wide band of spectral radiation giving whitelight. Since the individual lters in the filter disk permit only aportion of this spectral energy to be transmitted, it follows that theeiiciency of transfer of electron beam energy to useful light is greatlyreduced by the action of the filters.

According to the present inventiony however, the cathodoluminescent orcathode ray (C. R.) phosphor 56 is made of a material which, whenexcited by the electron beam, will produce a preponderance of radiantenergy in the ultraviolet region. The disk 60 instead of being providedwith color filters is then provided with a plurality of individualsecondary targets coated with a photoluminescent material excitable bythe ultraviolet radiated from the cathodoluminescent phosphor of theprimary target 5S. Each of these photoluminescent phosphor targets ismade of a material which emits a band of spectral energy correspondingto the red, blue or green lters of the transmitting scanning iiltersdiscussed in Figure 1. If then the secondary targets on thephotolurninescent target disk are placed immediately adjacent andpractically touching the ultraviolet-transmitting outer face oi thekinescope te, the ultraviolet produced by the phosphor 53 will excitethe individual photolurninescent targets to provide the desired red,blue or green images as the disk et revolves. The eye 62 will then, oicourse, combine the red, blue and green records thus produced to createa visual reconstruction of the color image iii. It will then be evidentthat with the arrangement provided by the present invention virtuallyall of the beam energy of the kinescope is is transformed indirectly toonly that band of spectral wavelengths needed for a given color record.Since the transormation enciency of electron beam energy to ultravioletand violet radiation by cathodolurninescent phosphors is quite high andthe transformation oi ultraviolet energy to visible energy byphotoluminescent phosphors is nearly 100 per cent on a quantum basis,the overall efficiency of the arrangement employing the presentinvention is niuch higher than obtainable in prior art systems. Thisprovides the eye with a much more brilliant cclor image for a givenvalue of beam power.

This embodiment of Figure 2 may be compared to the photographic processof making contact prints in that it is desired that the ultravioletima-ge produced by the cathodoluminescent phosphor on the kinescopescreen 5 be directly transferred tc the photoluminescent targets E2 inthe disk without any diiusion of the radiant energy rays emanating fromthe kineseope target. Home ever, in practice, it will be found that thethickness of the glass 5ft covering the screen 56 is sufciently greatthat the ultraviolet rays leaving the individual points of ultravioletradiation on the kinescope screen have considerable chance to dirnu fusebefore reaching the photolurninescent target This tends to reduce theresolution of the visible color record thereby produced.

Evidently, if the thickness of the kinescope is sufliciently small andthe spacing between the photoluminescent target 52 and the ace of thelineseope is small, the effect of diffusion may be negligible. lowever,in cases Where the face of the kinescope is made necessarily thick, thepresent invention contemplates the use of a plurality oi individualtransparent cylinders, such as 35, arranged in close-packed honeycombedfashion over the area of the kinescope screen. These cylinders may bemade of glass, quartz, or any other workable transparent material,formed and coated if required, to provide individual radi ant energyguides. These light guides will act over elemental areas of the primarytarget oi cathodolurninescent screen to conduct radiant energy from theinside of the kinescope to the outside of the kinescope. By the use or"such individual cellular light guides, the diffusion of the image due tothe thickness of the tube glass will he cut dei/vn greatly, thusly toimprove the resolution of the contact print made on the secondarytarget. As shown, these individual cellular light guides @E are arrangedwith their axes of transmission virtually perpendicular to the face ofthe tube and may, although shown circular in form,

assume any desired cross-sectional shape. One form of making such acellular screen covering for a kinescope is to cut a number of quartzcylinders of a very small diameter quartz rod. These individualcylinders may then be bundled and fused together with theirlongitudinally axes parallel to one another to form a suitable frontsurface for the kineseope 44. To seal any interstices existing betweenthe rods a thin vacuum tight glass or quartz layer may be placed on theouter surface or" the screen.

A front elevational view of the disk 60, provided with threephotoluminescent targets 62a, 52h, and t2@ in accordance with thepresent invention, is shown in Figure 3. For convenience, the

targets have been shown bounded by radii of the disc but of course mayin practice assume any desired shape.

An alternative arrangement for impressing the ultraviolet image formedby the kinescope target on the photoluminescent targets, such as 62, isshown in Figure 4. In this case, an optical lens system, such as 68,adapted to conduct ultraviolet rays without high attenuation, isinterposed between the screen surface of the kinescope lfl and thetarget 52. Although some loss in ultraviolet intensity will be sufferedthrough the use of lens the image produced on the photoluminescentphosphor target 52 in the disk 6&3 Will be much sharper than the contactprinting arrangementof Fig. 2 since diffusion of the light from thecathodoluminescent target 55 is no longer a problem. This latterarrangement in Fig. 4 also eliminates the need for rather costly andelaborate cellular light guide construction of the kinescope face ifdilusion is to be prevented in the contact printing method.

it will be clear from the foregoing that although, in accordance withthe present invention, the cathodoluminescent phosphor on the primarytarget or screen of the kinescope radiates energy having a peak in theultraviolet region, this cathodoluniinescent material may well be chosento emit some blue light so balanced to eliminate the need of a secondaryblue photoluminescent target in the disk eil. Accordingly, otherindividual hues could be imparted by the cathodoluminescent target whichcould be used to supplement or entirely replace other spectral bands notadequately represented by the photoluminescent phosphore.

In the practice or" the present invention, the following shortpersistent luminescent materials cited only by Way of example are ioundto be suitable for use as cath-odoluminescent phosphors:

ZnS Ag(700-1400 JC.) -Violet `and blue-emitting. A1203(1600 C.)Ultraviolet-emitting.

'ihis latter ZnS:Ag(700-1400 C.)blue emit-- ting cathodeluminescentmaterial may be employed as discussed above to render unnecessary the`provision of a blue photoluminescent phos phor, there being sufficientviolet and blue light emitted from the ZnSng phosphor to adequatelyl ZnSAg(700-1400 C.) Blue-emitting.

In general the phosphors chosen for application in practice of thepresent invention as shown in connection with the disc of Figure 3should have suiiiciently short phosphorescence 'to .prevent smearing orblurring of picture elements due to the rotation of the disc. For thisreason, the foregoing list of phosphore for the secondaryphotoluminescent targets may b-e expanded to include the manyshort-persistent organic luminescent materials such as blue-emittingaesculin or alloxazine, green-emitting malachite green or the zinc saltof B-hydroxyquinoline, and redemitting rhodamine B extra or crystalviolet.

It will be obvious to those familiar with the electronic art, as well asthose acquainted with the present-day X-ray tube techniques that thecolor disk carrying the secondary or photoluminescent targets could wellbe incorporated in the evacuated envelope housing the kinescope gunstructure. The color disk itself could be pivoted and rotated by a motorarrangement having its armature within the evacuated envelope androtating field-producing structure of the motor out side the kinescopeenvelope. This practice is common in the electronic art and in th-e caseof the present invention would permit the use of a thinner supportingmember for the cathodoluminescent target which of course provides betterdefinition in the contact printing of the color image.

It is further apparent that the present invention, although described inconnection with color television systems utilizing the additive primarycolors of red, blue and green, its utility is in no way limited thereto.The virtually three-fold increase in brilliance made available by thepresent invention over prior art systems is obtained in such a way as torender the present invention applicable to many other color imagereproducing systems utilizing diiierent numbers and types of additivecolor records.

Moreover, although the secondary photoluminescent phosphor targets havebeen shown as mounted in a rotating disk such that the visible lightproduced thereby is viewable from the surface of the photoluminescenttarget away from the ultraviolet izinescope screen, other opticalsystems, such as a Schmidt system, could be employed wherein the imageproduced on the photoluminescent target was picked up and utilized fromthe side of the secondary target adjacent the kinescope screen. Theactual optical arrangement employed is therefore a matter of choice andin no way eietcs the novel principles underlying the present invention.For example, a Schmidt optical system may well replace the refractiveoptical system of Fig. 4 with a considerable increase in efficiency. Itis clear, too, that although a kinescope has been shown as a source oiultraviolet and/or blue image color records, any suitable device iorproducing ultraviolet and/or blue images could be employed in the.practice of the present invention with equal success.

Having thus described my invention, what I claim is:

l. In a system in which a color image is to be reproduced by viewing aplurality of different complementary color records, means for producingimages of ultraviolet radiation representative of predeterminedcomponent color records of the color image, a plurality ofphotoluminescent targets each responsive to the ultraviolet radiation ofsaid image producing means to radiate a respective visible light imagecorresponding to a diierent complementary color record, means forfocussing said ultraviolet image ontov said photoluminescent targets,and means supporting said luminous targets in moving relation to saidimage source for eiectively combining the visible light images with oneanother to produce a composite color image.

2. Apparatus according to claim l wherein said means for producing saidultraviolet images also produce visible radiant energy falling withinpredetermined band ci wavelengths, and wherein the visible lightradiation characteristic of each of said photoluminescent target-s iscorrected to compensate for the visible radiation of said ultravioletimage producing means whereby to render a correct color balance in thecomposite color image.

3. Apparatus according to claim 1 wherein said means for producing saidultraviolet focussed images is also productive of visible light energycorresponding to a particular complementary color records and whereinsaid plurality of photoiuminescent targets are responsive to producevisible light image complementary color records which cooperate with thecolor record produced by said ultraviolet image producing means to forma balanced color image.

4. In a color image reproducing system, in combination, a cathode raygun structure for forming and directing an accelerated electron beam, acathodoluminescent primary target for said beam adapted to radiatepredetermined wavelength distribution of spectral energy when excited bysaid beam, a viewing device having a viewing surface divided into aplurality of separate viewing sections, each section having formedthereon a secondary target of photoluminescent material excitable by thepredetermined wavelengths radiated by said primary target to produce adifferent color component wavelength oi the color image to be formed,and means for sequentially presenting the individual sections of saidviewing device for excitation by radiant energy produced from saidprimary target.

5. Apparatus according to claim 4 wherein the cathodoluminescentcharacter of said primary target is such to radiate the largest energycomponent in the invisible ultraviolet region.

6. Apparatus according to claim 4 wherein the character of thecathodoluminescent primary target is such that the wavelengths of theradiation produced thereby fall into at least two groups, the iirstgroup in the invisible ultraviolet region and the second in the visiblecolor range corresponding to a color component of the image to beformed.

7. In a color image reproducing system, the combination of a cathode raygun assembly adapted to form and direct a deflectable acceleratedelectron beam, means for deilecting and for modulating the intensity ofsaid electron beam in accordance with scanned image information, aprimary target positioned such that one surface thereof intercepts saidbeam, a coating of cathodoluminescent material on the target suriaceintercepting said beam, the cathodolumines cent material being of a typeresponsive to said electron beam to radiate a predetermined wavelengthof spectral energy, a plurality of secondary targets each holding asurface photoluminescently responsive to the spectral energy radiated bysaid primary target, each photoluminescent surface in turn .soconstituted to secondarily radiate a different spectral visual colorcomponent of the color image to be reproduced, and means forsequentially directing the spectral energy of said primary target ontoeach of said plurality of secondary targets.

8. Apparatus according to claim 7 wherein the cathodoluminescentcharacter of said primary target is such to radiate the largest energycomponent in the invisible ultraviolet region.

9. Apparatus according to claim 7 wherein the character of thecathodoluminescent primary target is such that the wavelengths of theradiation produced thereby fall into at least two groups, the firstgroup in the invisible ultraviolet region and the second in the visiblecolor range corresponding to a colo-r component of the image to beformed.

10. Apparatus according to claim 7 wherein said cathode ray gun isenclosed in an evacuated envelope having a transparent window whoseinner surface supports said primary target and wherein said means forsequentially directing the spectral energy of said primary targetcomprises in combination, means for movably positioning said secondarytarget immediately adjacent and in virtual contact with the outersurface of said window.

11. Apparatus according to claim 10 wherein the transparent window ofthe evacuated envelope embraces a plurality of cellular light guideslongitudinally extending from the inner primary surface to the outersurface of said window.

12. Apparatus according to claim 7 wherein said cathode ray gun isenclosed in an evacuated envelope having a transparent window whoseinner surface supports said primary target, and wherein said means forsequentially directing the spectral energy of said primary targetcomprises an optical system for translating and focussing into an imageplane rays of wavelength corresponding to the radiation of said primarytarget, said optical system being positioned adjacent the window of saidenvelope, and means for selectively positioning said secondary targetsin the focussed image plane produced by said optical system.

13. Apparatus according to claim 10 wherein said secondary targets arefixed in a circular locus on a transparent base about a center ofrotation 10 for that base and wherein said optical combining meanscomprises means for rotationally driving said base about its center ofrotation at a position such that said secondary targets are moved'through the focussed image plane produced by said optical image.

14. In a color television receiver adapted to receive and demodulatepicture information for application to at least a first, second andthird color channel image reproducing system comprising a cathode raygun structure for forming and directing a deectable electron beam, meansfor sequentially deiiecting and modulating the intensity of saidelectron beam in accordance with image information communicated by saidfirst, second and third channels respectively, a primary targetpositioned su-ch that one surface thereof intercepts said beam, acoating of cathodoluminescent material on the target surfaceintercepting said beam, the cathodoluminescent material being of thetype responsive to said electron beam to radiate a predeterminedwavelength of spectral energy, a plurality of secondary targets eachholding a photolurninescent surface responsive to the spectral energyradiated by said primary target, each secondary target surface being inturn so constituted to secondarly radiate a different visual colorcomponent of the color image to be reproduced, said color componentscorresponding to the type of image information represented by saidfirst, second and third channels, and means for sequentially directingthe spectral energy of said primary target onto each of said pluralityof secondary targets.

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